This invention relates to wireless communication systems and, more particularly, to monitor and dynamically assign signal data rates for data services in such systems.
Wireless communication systems have been developed to allow transmission of information signals between an originating location and a destination location. Both analog (first generation) and digital (second generation) systems have been developed to transmit information signals over communication channels linking the source and destination locations. Digital methods tend to afford several advantages over analog systems. For example, improved immunity to channel noise and interference, increased capacity, and encryption for secure communications are advantages of digital systems over analog systems.
While first generation systems were primarily directed to voice communication, second generation systems support both voice and data applications. Numerous techniques are known in second-generation systems for handling data transmissions which have different transmission requirements. In particular, packet data transmission typically involves relatively short transmission duration whereas voice transmission is of a longer duration and requires continuous access to the communication channel. Several modulation/coding arrangements have been developed, such as frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA), to increase the number of users that can access a wireless network. CDMA systems are more immune to multiple path distortion and co-channel interference than FDMA and TDMA systems and reduce the burden of frequency/channel planning that is common with FDMA and TDMA systems.
In a CDMA system, a unique binary code sequence is assigned to each active user within a cell to uniquely identify the user and spread the user""s signal over a larger bandwidth. Multiplied by the assigned code, the user""s signal is spread over the entire channel bandwidth, which is wider than the user""s signal bandwidth. The ratio of the system channel bandwidth to the user""s bandwidth is the xe2x80x9cspreading gainxe2x80x9d of the system. The capacity of the CDMA system is proportional to the xe2x80x9cspreading gainxe2x80x9d for a given signal-to-interference (S/I) level. After reception of the transmitted signal, the signal of each user is separated, or de-spread, from the signal of other users by using a correlator keyed to the code sequence of the desired signal.
First-generation analog and second-generation digital systems were designed to support voice communication with limited data communication capabilities. Third-generation wireless systems, using wide-band multiple access technologies such as CDMA, are expected to effectively handle a large variety of services, such as voice, video, data and imaging. Among the features which will be supported by third-generation systems is the transmission of high-speed data between a mobile terminal and a land-line network. As is known, high-speed data communications is often characterized by a short transmission xe2x80x9cburstxe2x80x9d at a high data transmission rate, followed by some longer period of little or no transmission activity from the data source. To accommodate the bursty nature of such high-speed data services in third-generation systems, it is necessary for the communications system to assign a large bandwidth segment (corresponding to the high data rate) for the duration of the data burst from time to time. With the ability of the third generation systems to handle such bursty high-speed data transmission, throughput and delay for users can be advantageously improved. However, because of the large amount of instantaneous bandwidth required for transmission of a burst of high-speed data, the management of such bursts, and particularly the allocation of power and system resources thereto, must be handled with care to avoid unwarranted interference with other services using the same frequency allocation.
In a wireless system accommodating the transmission of large blocks of data, the highest data rates would naturally be assigned to a bulk transmission user. As doubling the data rate would require only one-half the time to complete the transmission, assigning the highest data rate to such a user would minimize the time to transmit the user""s data. However, as the number of users increases, and the information to be transmitted progresses from voice toward multimedia (real time video, and voice), the demands on the resources of the base station also increase. To insure that sufficient capacity exists to provide acceptable levels of service to the full user community, the communication systems must be capable of dynamically assigning system resources in an efficient and cost effective manner. U.S. Pat. No. 5,857,147, entitled, xe2x80x9cMethod and Apparatus for Determining the Transmission Data Rate in a Multi-User Communication System,xe2x80x9d to Gardner, et al., teaches of adjusting the data rates of a class of users in a muti-user signal environment such that the acceptable overall signal quality is maintained for the class of users.
As new users request entry onto the wireless network, a communication system base station must determine the resources necessary to accommodate the needs of the user and must allocate these resources to the user. Should sufficient resources be unavailable to accommodate the user, the base station must delay establishing a connection with the user and the user must wait until sufficient resources become available.
Among the resources the base station must allocate in establishing a communication link to a user are output power and data rate. Output power and data rate are proportionally relatedxe2x80x94the output power necessary to establish or maintain a link with a user increasing as the data rate increases. This increase in output power with increasing data rate is required to maintain the output energy per bit at a constant level. As base stations have limited output power resources, a base station must balance the transmission needs of its users, individually and collectively, against the base station""s own output power limitations.
Thus, upon a request for entry to the wireless network by a user, the base station must evaluate the user""s data rate and power demands against the current user environment and power demands. As the user environment approaches the total system capacity, the base station must delay the entry of a user onto the system to prevent overloading the output power capability of the base station. For example, a base station processing multiple users, each requiring high data rates, may be incapable of honoring a request for access by an additional low rate data user, because the base station lacks the power to meet the requirements of the additional low rate data user. This power deficiency may not be caused by the number of users in the system but rather by an excessive expenditure of power related to an inefficient allocation of data rates to the users. Assigning users with data rates significantly above that which is necessary to meet the users"" immediate needs, wastes system resources, reduces the number of user capable of having concurrent access to the system, and increases the delay a user experiences in accessing the network. Thus, there is a need to efficiently manage and utilize the base station resources in order to provide users with a minimum data rate, and corresponding reduced power, that is just sufficient to meet their transmission needs.
It is an object of the invention to assign transmission data rates for a wireless system in an efficient manner by dynamic determination of the user""s transmission needs during an active data session. It is a further object of the invention to dynamically adjust the transmission data rates by monitoring the transmission data buffers during an active data session. It is a further object of the invention to dynamically adjust and maintain assigned transmission data rates at a minimum necessary to fulfill the needs of the users.
The invention employs a fixed rate, low speed channel, which may be a control or signalling channel, to transmit user data up to the data rate of the channel and further operates to determine when a higher speed data link must be employed to meet the user""s transmission requirements. In carrying out this function, the invention monitors the quantity of data within the transmit and receive data buffers during an active data session. Each buffer is monitored separately from the other and, also, separately or each active user served by that base station. When the quantity of data in the transmit or receive buffer exceeds predetermined threshold values, a higher speed data rate is established, using a supplemental data channel, to enable the base station to maintain the data buffers within prescribed threshold levels. Similarly, should the level of data in the data buffers fall below desired threshold levels, indicating the offered data rate is higher than is necessary for the user, a lower speed data rate is employed. Thus, each user is assigned the minimum data rate necessary to transmit data between the base station and the user at the remote site.